EP3494158B1 - Semi-crystalline thermoplastic polyester for producing bioriented films - Google Patents

Description

Field of the invention

The present invention relates to the use of a semi-crystalline thermoplastic polyester comprising at least one 1,4: 3,6-dianhydrohexitol unit which has excellent properties for the manufacture of bi-oriented films.

Technological background of the invention

Plastics have become essential for mass production of objects. Indeed, their thermoplastic nature allows these materials to be transformed at high speed into all kinds of objects.

Certain thermoplastic aromatic polyesters have thermal properties allowing them to be used directly for the manufacture of materials. They include aliphatic diol and aromatic diac units. Among these aromatic polyesters, mention may be made of polyethylene terephthalate (PET), which is a polyester comprising ethylene glycol and terephthalic acid units, used for example in the manufacture of bi-oriented films.

However, for certain applications or under certain conditions of use, it is necessary to improve certain properties and in particular impact resistance or thermal resistance. This is how modified glycol PETs (PETg) were developed. These are generally polyesters comprising, in addition to ethylene glycol and terephthalic acid units, cyclohexanedimethanol units (CHDM). The introduction of this diol into PET allows it to adapt the properties to the intended application, for example to improve its impact resistance or its optical properties.

Other modified PETs have also been developed by introducing 1,4: 3,6-dianhydrohexitol units into the polyester, in particular isosorbide (PEIT). These modified polyesters have higher glass transition temperatures than unmodified PETs or PETg comprising CHDM. In addition, 1,4: 3,6-dianhydrohexitols have the advantage that they can be obtained from renewable resources such as starch. One problem with these PEITs is that they may have insufficient impact resistance properties. In addition, the glass transition temperature may be insufficient for the manufacture of certain plastic objects.

To improve the impact resistance properties of polyesters, it is known in the prior art to use polyesters whose crystallinity has been reduced. As regards polyesters based on isosorbide, mention may be made of the application US2012 / 0177854 which describes polyesters comprising terephthalic acid units and diol units comprising from 1 to 60 mol% of isosorbide and from 5 to 99% of 1,4-cyclohexanedimethanol which exhibit improved impact resistance properties. As indicated in the introductory part of this application, it is a question of obtaining polymers from which the crystallinity is eliminated by the addition of comonomers, and therefore here by the addition of 1,4-cyclohexanedimethanol. In the examples section is described the manufacture of different poly (ethylene-co-1,4-cyclohexanedimethylene-co-isosorbide) terephthalates (PECIT) as well as an example of poly (1,4-cyclohexanedimethylene-co-isosorbide) terephthalate (PCIT).

It can also be noted that, while PECIT type polymers have been the subject of commercial developments, this is not the case with PCITs. In fact, their manufacture has hitherto been considered as complex, the isosorbide having a low reactivity as a secondary diol. Yoon et al. (Synthesis and Characteristics of a Biobased High-Tg Terpolyester of Isosorbide, Ethylene Glycol, and 1,4-Cyclohexane Dimethanol: Effect of Ethylene Glycol as a Chain Linker on Polymerization, Macromolecules, 2013, 46, 7219-7231 ) have thus shown that the synthesis of PCIT is much more difficult to achieve than that of PECIT. This document describes the study of the influence of the ethylene glycol level on the kinetics of PECIT manufacturing.

In Yoon et al., An amorphous PCIT (which comprises about 29% isosorbide and 71% CHDM compared to the sum of the diols), is manufactured in order to compare its synthesis and its properties with those of PECIT type polymers. The use of high temperatures during the synthesis induces a thermal degradation of the polymer formed if one refers to the first paragraph of the Synthesis part of page 7222, this degradation being notably linked to the presence of cyclic aliphatic diols such as isosorbide . Therefore , Yoon et al. have used a process in which the polycondensation temperature is limited to 270 ° C. Yoon et al. have found that, even by increasing the polymerization time, the process also does not make it possible to obtain a polyester having a sufficient viscosity. Thus, without the addition of ethylene glycol, the viscosity of the polyester remains limited, this despite the use of extended synthesis times.

Thus, despite the modifications made to PETs, there is still a constant need for new polyesters having improved properties.

In the field of plastics, and in particular for the manufacture of bi-oriented films, it is necessary to have semi-crystalline thermoplastic polyester with improved properties which make it possible to obtain bi-oriented films having better thermal resistance as well as improved mechanical properties such as threshold stress and tear resistance.

We know of the document US6126992 objects made from polymers having terephthalic acid units, ethylene glycol units and isosorbide units and optionally another diol (for example 1,4-cyclohexanedimethanol). All of the polymers obtained thus have ethylene glycol units because it is widely accepted that the latter are necessary for the incorporation of isosorbide and for obtaining a high glass transition temperature. In addition, the examples of preparation used do not make it possible to obtain polymers with a pattern composition making it possible to give complete satisfaction in the manufacture of bi-oriented films. Indeed, Example 1 describes in particular the preparation of a polymer comprising 33.5% of ethylene glycol unit and 12.9% of isosorbide unit, ie an isosorbide unit / ethylene glycol unit ratio of 0.39 which is not not convincing for the production of bi-oriented films.

The document US5958581 describes bi-oriented polyester films made from a polymer having isosorbide units, terephthalic acid units, and ethylene glycol units. The bi-oriented films thus produced are suitable for use in particular as food packaging or as an insulator. The document WO 2013/136875 A1 describes the preparation of bi-oriented polyester films. Example 2 describes the preparation of a bi-oriented polyester film from isosorbide, cyclohexane-dimethanol, ethylene glycol and dimethyl terephthalate. The mole share of ethylene glycol is less than 5%. The reduced viscosity in solution is 66 mL / g.

Thus, there is still today the need for semi-crystalline thermoplastic polyesters containing 1,4: 3,6-dianhydrohexitol units for the production of bi-oriented films, said polyesters making it possible to obtain bi-oriented films having improved mechanical properties.

It is therefore to the credit of the Applicant to have found that this objective could, against all odds, be achieved with a semi-crystalline thermoplastic polyester based on isosorbide having no ethylene glycol when it was known until now that the latter was essential for the incorporation of said isosorbide. Indeed, the semi-crystalline thermoplastic polyester used according to the present invention, thanks to a viscosity and a ratio in particular pattern, has improved properties for use according to the invention in the manufacture of bi-oriented films.

Summary of the invention

• au moins un motif 1,4 : 3,6-dianhydrohexitol (A) ;
• au moins un motif diol alicyclique (B) autre que les motifs 1,4 : 3,6-dianhydrohexitol (A) ;
• au moins un motif acide téréphtalique (C) ;

dans lequel le ratio (A)/[(A)+(B)] étant d'au moins 0,05 et d'au plus 0,30 ;
ledit polyester étant exempt de motifs diol aliphatique non cyclique ou comprenant une quantité molaire de motifs diol aliphatique non cyclique, par rapport à la totalité des motifs monomériques du polyester, inférieure à 5%, et dont la viscosité réduite en solution (25°C ; phénol (50%m) : ortho-dichlorobenzène (50%m) ; 5 g/L de polyester) est supérieure à 50 mL/g.The subject of the invention is therefore the use of a semi-crystalline thermoplastic polyester for the manufacture of bi-oriented films, said polyester comprising:

• at least one 1,4: 3,6-dianhydrohexitol unit (A);
• at least one alicyclic diol unit (B) other than 1,4: 3,6-dianhydrohexitol units (A);
• at least one terephthalic acid unit (C);

wherein the ratio (A) / [(A) + (B)] being at least 0.05 and at most 0.30;
said polyester being free of non-cyclic aliphatic diol units or comprising a molar quantity of non-cyclic aliphatic diol units, relative to the totality of the monomeric units of polyester, of less than 5%, and whose reduced viscosity in solution (25 ° C; phenol (50% m): ortho-dichlorobenzene (50% m); 5 g / L of polyester) is greater than 50 mL / g.

A second object of the invention relates to a process for manufacturing bi-oriented films based on the semi-crystalline thermoplastic polyester described above.

Finally, a third object of the invention relates to a bi-oriented film comprising the previously described semi-crystalline thermoplastic polyester.

These semi-crystalline thermoplastic polyesters offer excellent properties and in particular make it possible to manufacture bi-oriented films having better thermal resistance and improved mechanical properties.

Detailed description of the invention

• au moins un motif 1,4 : 3,6-dianhydrohexitol (A) ;
• au moins un motif diol alicyclique (B) autre que les motifs 1,4 : 3,6-dianhydrohexitol (A) ;
• au moins un motif acide téréphtalique (C) ;

dans lequel le ratio molaire (A)/[(A)+(B)] étant d'au moins 0,05 et d'au plus 0,30 et la viscosité réduite en solution supérieure à 50 mL/g.A first object of the invention relates to the use of a semi-crystalline thermoplastic polyester for the manufacture of bi-oriented films, said polyester comprising:

• at least one 1,4: 3,6-dianhydrohexitol unit (A);
• at least one alicyclic diol unit (B) other than 1,4: 3,6-dianhydrohexitol units (A);
• at least one terephthalic acid unit (C);

wherein the molar ratio (A) / [(A) + (B)] being at least 0.05 and at most 0.30 and the reduced viscosity in solution greater than 50 mL / g.

By “molar ratio (A) / [(A) + (B)]” is meant the molar ratio of 1,4: 3,6-dianhydrohexitol units (A) / sum of 1,4: 3,6-dianhydrohexitol units ( A) and alicyclic diol units (B) other than 1,4: 3,6-dianhydrohexitol units (A).

The semi-crystalline thermoplastic polyester is free from or comprises a small amount of non-cyclic aliphatic diol units.

By “low molar quantity of non-cyclic aliphatic diol units” is meant in particular a molar quantity of non-cyclic aliphatic diol units of less than 5%. According to the invention, this molar amount represents the ratio of the sum of the non-cyclic aliphatic diol units, these units possibly being identical or different, relative to all of the monomeric units of the polyester.

A non-cyclic aliphatic diol can be a linear or branched non-cyclic aliphatic diol. It can also be a saturated or unsaturated non-cyclic aliphatic diol. In addition to ethylene glycol, the saturated linear non-cyclic aliphatic diol can for example be 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8- octanediol and / or 1,10-decanediol. As an example of a saturated branched non-cyclic aliphatic diol, mention may be made of 2-methyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-2-butyl-1, 3-propanediol, propylene glycol and / or neopentylglycol. As an example of an unsaturated aliphatic diol, mention may, for example, be made of cis-2-butene-1,4-diol.

This molar amount of non-cyclic aliphatic diol unit is advantageously less than 1%. Preferably, the polyester is free of non-cyclic aliphatic diol unit and more preferably, it is free of ethylene glycol.

Despite the small amount of non-cyclic aliphatic diol, and therefore ethylene glycol, used for the synthesis, there is surprisingly obtained a semi-crystalline thermoplastic polyester having a reduced viscosity in high solution and in which the isosorbide is particularly well incorporated. Without being bound by any theory, this would be explained by the fact that the reaction kinetics of ethylene glycol is much higher than that of 1,4: 3,6-dianhydrohexitol which strongly limits the integration of this last in polyester. The resulting polyesters therefore have a low integration rate of 1,4: 3,6-dianhydrohexitol and therefore a relatively low glass transition temperature.

The monomer (A) is a 1,4: 3,6-dianhydrohexitol can be isosorbide, isomannide, isoidide, or a mixture thereof. Preferably, 1,4: 3,6-dianhydrohexitol (A) is isosorbide.

Isosorbide, isomannide and isoidide can be obtained by dehydration of sorbitol, mannitol and iditol respectively. As regards isosorbide, it is marketed by the Applicant under the brand name POLYSORB® P.

The alicyclic diol (B) is also called the aliphatic and cyclic diol. It is a diol which can in particular be chosen from 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol or a mixture of these diols. Very preferably the alicyclic diol (B) is 1,4-cyclohexanedimethanol. The alicyclic diol (B) can be in the cis configuration, in the trans configuration or can be a mixture of diols in the cis and trans configuration .

The molar ratio of 1,4: 3,6-dianhydrohexitol units (A) / sum of 1,4: 3,6-dianhydrohexitol units (A) and alicyclic diol units (B) other than 1,4: 3 units, 6-dianhydrohexitol (A), or (A) / [(A) + (B)], is at least 0.05 and at most 0.30. Advantageously, this ratio is at least 0.1 and at most 0.28, and very particularly this ratio is at least 0.15 and at most 0.25.

• une quantité molaire de motifs 1,4 : 3,6-dianhydrohexitol (A) allant de 2,5 à 14 % mol ;
• une quantité molaire de motifs diol alicyclique (B) autre que les motifs 1,4 : 3,6-dianhydrohexitol (A) allant de 31 à 42,5 % mol ;
• une quantité molaire de motifs acide téréphtalique (C) allant de 45 à 55 % mol.

A semi-crystalline thermoplastic polyester particularly suitable for the manufacture of bi-oriented films comprises:

• a molar quantity of 1,4: 3,6-dianhydrohexitol (A) units ranging from 2.5 to 14 mol%;
• a molar amount of alicyclic diol units (B) other than the 1,4: 3,6-dianhydrohexitol units (A) ranging from 31 to 42.5 mol%;
• a molar amount of terephthalic acid units (C) ranging from 45 to 55 mol%.

The amounts of different units in the polyester can be determined by 1 H NMR or by chromatographic analysis of the mixture of monomers resulting from methanolysis or from complete hydrolysis of the polyester, preferably by ¹ H NMR.

Those skilled in the art can easily find the analysis conditions for determining the amounts of each of the polyester units. For example, from an NMR spectrum of a poly (1,4-cyclohexanedimethylene-co-isosorbide terephthalate), the chemical shifts relative to 1,4-cyclohexanedimethanol are between 0.9 and 2.4 ppm and 4 , 0 and 4.5 ppm, the chemical shifts relating to the terephthalate cycle are between 7.8 and 8.4 ppm and the chemical shifts relating to the isosorbide are between 4.1 and 5.8 ppm. The integration of each signal makes it possible to determine the quantity of each pattern of the polyester.

The semi-crystalline thermoplastic polyesters used according to the invention have a melting temperature ranging from 210 to 295 ° C, for example from 240 to 285 ° C.

In addition, the semi-crystalline thermoplastic polyesters have a glass transition temperature ranging from 85 to 120 ° C, for example from 90 to 115 ° C. The glass transition and melting temperatures are measured by conventional methods, in particular by using differential scanning calorimetry (DSC) using a heating rate of 10 ° C./min. The experimental protocol is detailed in the examples section below.

Advantageously, the semi-crystalline thermoplastic polyester has a heat of fusion greater than 10 J / g, preferably greater than 20 J / g, the measurement of this heat of fusion consisting in subjecting a sample of this polyester to a heat treatment at 170 ° C for 16 hours then evaluate the heat of fusion by DSC by heating the sample to 10 ° C / min.

The semi-crystalline thermoplastic polyester used according to the invention has in particular a clarity L * greater than 40. Advantageously, the clarity L * is greater than 55, preferably greater than 60, most preferably greater than 65, for example greater than 70. The L * parameter can be determined using a spectrophotometer, using the CIE Lab model.

Finally, the reduced viscosity in solution of said semi-crystalline thermoplastic polyester is greater than 50 ml / g and preferably less than 150 ml / g, this viscosity being able to be measured using an Ubbelohde capillary viscometer at 25 ° C. an equimassic mixture of phenol and ortho-dichlorobenzene after dissolution of the polymer at 130 ° C. with stirring, the concentration of polymer introduced being 5 g / L.

This test for measuring reduced viscosity in solution is, by the choice of solvents and the concentration of polymers used, perfectly suited for determining the viscosity of the viscous polymer prepared according to the process described below.

The semi-crystalline nature of the thermoplastic polyesters used according to the present invention is characterized when the latter, after a heat treatment of 16 h at 170 ° C., exhibit X-ray diffraction lines or an endothermic melting peak in Differential Calorimetric Analysis at Scanning (DSC).

The semi-crystalline thermoplastic polyester as defined above has many advantages for the production of bi-oriented films.

Indeed, thanks in particular to the molar ratio of 1,4: 3,6-dianhydrohexitol units (A) / sum of the 1,4: 3,6-dianhydrohexitol units (A) and alicyclic diol units (B) other than units 1 , 4: 3,6-dianhydrohexitol (A) of at least 0.05 and at most 0.30 and at a reduced viscosity in solution greater than 50 ml / g and preferably less than 150 ml / g, the semi-crystalline thermoplastic polyesters make it possible to manufacture bi-oriented films having better thermal resistance and improved mechanical properties compared for example to bi-oriented films made from conventional polyethylene isosorbide terephthalate (PEIT).

The difference between a bi-oriented film and a sheet lies in the thickness as such. However, no industrial standard precisely defines the thickness beyond which a sheet is considered to be a bi-oriented film. Thus, according to the present invention, a bi-oriented film is defined as having a thickness of less than 250 μm. Preferably, the bi-oriented films have a thickness of 5 μm to 250 μm, particularly from 10 μm to 50 μm and even more particularly from 10 μm to 25 μm, for example around 15 μm.

The bi-oriented films according to the invention can be directly manufactured from the molten state after polymerization of the semi-crystalline thermoplastic polyester.

According to an alternative, the semi-crystalline thermoplastic polyester can be packaged in an easily manipulated form such as pellets or granules before being used for the manufacture of bi-oriented films. Preferably, the semi-crystalline thermoplastic polyester is packaged in the form of granules, said granules being advantageously dried before processing in the form of bi-oriented films. The drying is carried out so as to obtain granules having a residual moisture content of less than 300 ppm, preferably less than 200 ppm, for example around 180 ppm. The bi-oriented films produced can be monolayer bi-oriented films or multilayer bi-oriented films obtained for example by laminating several layers, at least one of which contains a semi-crystalline thermoplastic polyester according to the invention.

The bi-oriented films made from the semi-crystalline thermoplastic polyester according to the invention can be obtained by methods known to those skilled in the art such as, for example, extrusion by flat die or also by annular die (inflation extrusion). Preferably, the bi-oriented films are produced by the flat die extrusion method.

The manufacture of bi-oriented film via extrusion by flat die, called extrusion cast, consists in stretching along two axes a flat sheet at the extruder outlet. In a particularly advantageous manner, this extrusion is carried out by means of a Stenter process which makes it possible to obtain bi-oriented films by sequential biorirection. The Stenter process takes place in three stages.

The first step consists in manufacturing a primary film obtained after extrusion through a flat die, stretched in the air for a short distance and then cooled on a thermostated roller, submerged or not in water. The film thus obtained has an average thickness of approximately 500 μm. The second step is to perform a first stretch in the machine direction (longitudinal) by passing the film over a series of preheating rollers before being stretched between two rollers rotating at different speeds. The film obtained after this second then has a thickness of approximately 100 μm. Finally, the third step consists in carrying out a second stretching in transverse direction. Thus, the mono-stretched film obtained in the previous step is gripped by clamps circulating on rails which move away from each other, the assembly being positioned in a hot air oven. The bi-oriented film obtained can thus have a thickness of approximately 20 μm.

The manufacture of bi-oriented films can also be carried out by extrusion-inflation and therefore consists in extruding the material in an annular die and simultaneously stretching it in both directions by the combined action of drawing and blowing. The tubular sheaths thus obtained have a thickness between 10 and 300 μm and a perimeter which ranges from a few centimeters to more than 10 meters. The extrusion axis can be vertical or horizontal, with balloon heights of up to 20 meters.

According to this method, a thin sheath is extruded, pinched and inflated with air which fills the sheath by the axis of the die head. A first radial stretch is thus carried out by inflation. The sheath is then cooled, then stretched longitudinally by drawing rollers.

According to a particular embodiment, the semi-crystalline thermoplastic polyester previously defined is used in combination with one or more additional polymers for the production of bi-oriented films.

The additional polymer can be chosen from polyamides, polyesters other than polyester according to the invention, polystyrene, styrene copolymers, styrene-acrylonitrile copolymers, styrene-acrylonitrile-butadiene copolymers, polymethyl methacrylates, copolymers acrylics, poly (ether-imides), polyphenylene oxides such as poly (2,6-dimethylphenylene), phenylene polysulfate, poly (ester-carbonates), polycarbonates, polysulfones, polysulfone ethers, polyether ketones and mixtures of these polymers.

The additional polymer can also be a polymer making it possible to improve the impact properties of the polymer, in particular functional polyolefins such as functionalized ethylene or propylene polymers and copolymers, core-shell copolymers or block copolymers.

One or more additives can also be added during the manufacture of the bi-oriented film from the semi-crystalline thermoplastic polyester in order to give it specific properties.

Thus, by way of example of an additive, mention may be made of fillers or fibers of organic or inorganic nature, nanometric or not, functionalized or not. It can be silica, zeolites, fibers or glass beads, clays, mica, titanates, silicates, graphite, calcium carbonate, carbon nanotubes, wood fibers, carbon fibers, polymer fibers , proteins, cellulosic fibers, lignocellulosic fibers and unstructured granular starch. These fillers or fibers can make it possible to improve the hardness, the rigidity or the permeability to water or to gases.

The additive can also be chosen from opacifying agents, dyes and pigments. They can be chosen from cobalt acetate and the following compounds: HS-325 Sandoplast® RED BB (which is a compound carrying an azo function also known under the name Solvent Red 195), HS-510 Sandoplast® Blue 2B which is an anthraquinone, Polysynthren® Blue R, and Clariant® RSB Violet.

The additive can also be a UV resistance agent such as, for example, benzophenone or benzotriazole type molecules, such as the Tinuvin ™ range from BASF: tinuvin 326, tinuvin P or tinuvin 234 for example or hindered amines such as the Chimassorb ™ range BASF: Chimassorb 2020, Chimasorb 81 or Chimassorb 944 for example.

The additive can also be a flame retardant or flame retardant, such as for example halogenated derivatives or non-halogenated flame retardants (for example phosphorus derivatives, such as Exolit® OP) or as the range of melamine cyanurates (for example melapur ™ example: melapur 200) or aluminum or magnesium hydroxides.

Finally, the additive can also be an antistatic agent or even an anti-block agent such as derivatives of hydrophobic molecules, for example Croda's Incroslip ™ or Incromol ™.

The bi-oriented film comprising the semi-crystalline thermoplastic polyester can also undergo additional treatments making it possible to improve its properties. As an example of additional treatments, mention may in particular be made of corona treatment, metallization treatment or even plasma treatment.

The corona treatment allows, via the ionization of the air thanks to a high frequency and high voltage electric arc, to create microporosities on the surface of the bi-oriented film allowing in particular the inks and glues to adhere better. Thus treated, bi-oriented films find a very particular application for packaging.

The metallization treatment makes it possible, via evaporation of aluminum under vacuum, to condense an aluminum layer of a few nanometers to a few tens of nanometers on the surface of the bi-oriented film which is then cooled to prevent it from melting. This treatment allows to opacify the bi-oriented film and thus limit the penetration of light which is particularly advantageous to avoid distorting the properties of any content.

Finally, plasma treatment consists in using the technology of atmospheric plasma deposition in order to treat the extreme surface (a few nm) of the bi-oriented film and to allow the selective grafting of chemical functions. This selective grafting can thus provide an anti-adhesive or promoter effect for adhesion to the bi-oriented film.

The use according to the present invention of semi-crystalline thermoplastic polyester for the manufacture of bi-oriented films is particularly advantageous.

Indeed, the bi-oriented films thus manufactured from semi-crystalline thermoplastic polyester whose molar ratio of 1,4: 3,6-dianhydrohexitol units (A) / sum of 1,4: 3,6-dianhydrohexitol units (A ) and alicyclic diol units (B) other than 1,4: 3,6-dianhydrohexitol units (A) being at least 0.05 and at most 0.30 and whose reduced viscosity in solution is greater at 50 mL / g, have remarkable properties, both from the point of view of mechanical properties, optical quality and also in terms of gas permeability.

Indeed, the bi-oriented films obtained have an improvement in thermal resistance, resulting in particular in an increase in the drawing rate of the assemblies for the complexed bi-oriented films as well as by a greater temperature range of use. than the usual bi-oriented films obtained with PET.

The bi-oriented films obtained according to the invention also have an improvement in mechanical properties such as the tensile modulus, the stress at the threshold and the resistance to tearing. These improvements make it possible to offer more resistant solutions, in particular for the packaging market, and better protection of products by improving secondary packaging.

The bi-oriented films manufactured according to the invention will thus find a very particular use for food applications thanks to their barrier properties with respect to flavors and thanks to their possibility of use hot and cold, in particular for freezing.

• Fourniture d'un polyester thermoplastique semi-cristallin tel que défini ci-dessus.
• Préparation dudit film bi-orienté à partir du polyester thermoplastique semi-cristallin obtenu à l'étape précédente.

A second object of the invention relates to a process for manufacturing a bi-oriented film, said process comprising the following steps:

• Supply of a semi-crystalline thermoplastic polyester as defined above.
• Preparation of said bi-oriented film from the semi-crystalline thermoplastic polyester obtained in the previous step.

The preparation step can be carried out by methods known to those skilled in the art which conventionally used for the manufacture of bi-oriented films.

Thus by way of example, the preparation step can be carried out by the method of extrusion by flat die or also by annular die (inflation extrusion). Preferably, the preparation step is carried out by the extrusion method by flat die, called cast extrusion, and in particular by a Stenter process.

A third object of the invention relates to a bi-oriented film comprising the semi-crystalline thermoplastic polyester described above. The bi-oriented film according to the invention can also comprise an additional polymer and / or one or more additives as defined above.

• une étape d'introduction dans un réacteur de monomères comprenant au moins un 1,4 : 3,6-dianhydrohexitol (A), au moins un diol alicyclique (B) autre que les 1,4 : 3,6-dianhydrohexitols (A) et au moins un acide téréphtalique (C), le ratio molaire ((A)+(B))/(C) allant de 1,05 à 1,5, lesdits monomères étant exempts de diol aliphatique non cyclique ou comprenant, par rapport à la totalité des monomères introduits, une quantité molaire de motifs diol aliphatique non cyclique inférieure à 5% ;
• une étape d'introduction dans le réacteur d'un système catalytique ;
• une étape de polymérisation desdits monomères pour former le polyester, ladite étape consistant en :
  • ▪ un premier stade d'oligomérisation pendant lequel le milieu réactionnel est agité sous atmosphère inerte à une température allant de 265 à 280°C, avantageusement de 270 à 280°C, par exemple 275°C ;
  • ▪ un second stade de condensation des oligomères pendant lequel les oligomères formés sont agités sous vide à une température allant de 278 à 300°C afin de former le polyester, avantageusement de 280 à 290°C, par exemple 285°C ;
• une étape de récupération du polyester thermoplastique semi-cristallin.

The semi-crystalline thermoplastic polyester particularly suitable for the manufacture of bi-oriented films can be prepared by a synthesis process comprising:

• a step of introduction into a reactor of monomers comprising at least one 1,4: 3,6-dianhydrohexitol (A), at least one alicyclic diol (B) other than 1,4: 3,6-dianhydrohexitols (A) and at least one terephthalic acid (C), the molar ratio ((A) + (B)) / (C) ranging from 1.05 to 1.5, said monomers being free of non-cyclic aliphatic diol or comprising, relative to all of the monomers introduced, a molar amount of non-cyclic aliphatic diol units of less than 5%;
• a step of introducing a catalytic system into the reactor;
• a step of polymerizing said monomers to form polyester, said step consisting of:
  • ▪ a first oligomerization stage during which the reaction medium is stirred under an inert atmosphere at a temperature ranging from 265 to 280 ° C, advantageously from 270 to 280 ° C, for example 275 ° C;
  • ▪ a second stage of condensation of the oligomers during which the oligomers formed are stirred under vacuum at a temperature ranging from 278 to 300 ° C in order to form the polyester, advantageously from 280 to 290 ° C, for example 285 ° C;
• a step of recovering the semi-crystalline thermoplastic polyester.

This first stage of the process takes place in an inert atmosphere, that is to say in an atmosphere of at least one inert gas. This inert gas can in particular be dinitrogen. This first stage can be carried out under a gas flow and it can also be carried out under pressure, for example at a pressure of between 1.05 and 8 bars.

Preferably, the pressure ranges from 3 to 8 bars, most preferably from 5 to 7.5 bars, for example 6.6 bars. Under these preferred pressure conditions, the reaction of all of the monomers with one another is favored by limiting the loss of monomers during this stage.

Prior to the first stage of oligomerization, a stage of deoxygenation of the monomers is preferably carried out. It can be done for example once the monomers have been introduced into the reactor, by producing a vacuum and then introducing an inert gas such as nitrogen. This vacuum-introduction cycle of inert gas can be repeated several times, for example from 3 to 5 times. Preferably, this vacuum-nitrogen cycle is carried out at a temperature between 60 and 80 ° C. so that the reagents, and in particular the diols, are completely melted. This deoxygenation step has the advantage of improving the coloring properties of the polyester obtained at the end of the process.

The second stage of condensation of the oligomers takes place under vacuum. The pressure can decrease during this second stage continuously by using pressure drop ramps, in stages or by using a combination of pressure drop ramps and steps. Preferably, at the end of this second stage, the pressure is less than 10 mbar, most preferably less than 1 mbar.

The first stage of the polymerization stage preferably has a duration ranging from 20 minutes to 5 hours. Advantageously, the second stage has a duration ranging from 30 minutes to 6 hours, the start of this stage consisting in the moment when the reactor is placed under vacuum, that is to say at a pressure of less than 1 bar.

The method further comprises a step of introducing a catalytic system into the reactor. This step can take place before or during the polymerization step described above.

The term “catalytic system” is understood to mean a catalyst or a mixture of catalysts, optionally dispersed or fixed on an inert support.

The catalyst is used in suitable quantities to obtain a high viscosity polymer in accordance with the use according to the invention for the manufacture of bi-oriented films.

An esterification catalyst is advantageously used during the oligomerization stage. This esterification catalyst can be chosen from tin, titanium, zirconium, hafnium, zinc, manganese, calcium, strontium derivatives, organic catalysts such as para-toluene sulfonic acid (APTS ), methane sulfonic acid (AMS) or a mixture of these catalysts. By way of example of such compounds, mention may be made of those given in the application. US2011282020A1 in paragraphs [0026] to [0029], and on page 5 of the application WO 2013/062408 A1 .

Preferably, in the first transesterification stage, a zinc derivative or a manganese derivative of tin or germanium is used.

As an example of mass quantities, it is possible to use from 10 to 500 ppm of metal contained in the catalytic system during the oligomerization stage, relative to the quantity of monomers introduced.

At the end of transesterification, the catalyst of the first stage can be optionally blocked by the addition of phosphorous acid or phosphoric acid, or else as in the case of tin (IV) reduced by phosphites such as phosphite triphenyl or phosphite tris (nonylephenyle) or those cited in paragraph [0034] of the application US2011282020A1 .

The second stage of condensation of the oligomers can optionally be carried out with the addition of a catalyst. This catalyst is advantageously chosen from tin derivatives, preferably tin, titanium, zirconium, germanium, antimony, bismuth, hafnium, magnesium, cerium, zinc, cobalt, iron, manganese, calcium, strontium, sodium, potassium, aluminum, lithium or a mixture of these catalysts. Examples of such compounds can be for example those given in the Patent EP 1,882,712 B1 in paragraphs [0090] to [0094].

Preferably, the catalyst is a derivative of tin, titanium, germanium, aluminum or antimony.

As an example of mass quantities, it is possible to use from 10 to 500 ppm of metal contained in the catalytic system during the stage of condensation of the oligomers, relative to the quantity of monomers introduced.

Most preferably, a catalytic system is used during the first stage and the second stage of polymerization. Said system advantageously consists of a catalyst based on tin or a mixture of catalysts based on tin, titanium, germanium and aluminum.

By way of example, a mass quantity of 10 to 500 ppm of metal contained in the catalytic system can be used, relative to the quantity of monomers introduced.

According to the preparation process, an antioxidant is advantageously used during the monomer polymerization step. These antioxidants make it possible to reduce the coloration of the polyester obtained. The antioxidants can be primary and / or secondary antioxidants. The primary antioxidant can be a sterically hindered phenol such as the compounds Hostanox® 0 3, Hostanox® 0 10, Hostanox® 0 16, Ultranox® 210, Ultranox®276, Dovernox® 10, Dovernox® 76, Dovernox® 3114 , Irganox® 1010, Irganox® 1076 or a phosphonate such as Irgamod® 195. The secondary antioxidant can be trivalent phosphorus compounds such as Ultranox® 626, Doverphos® S-9228, Hostanox® P-EPQ, or Irgafos 168.

It is also possible to introduce, as polymerization additive into the reactor, at least one compound capable of limiting the parasitic etherification reactions such as sodium acetate, tetramethylammonium hydroxide or tetraethylammonium hydroxide.

Finally, the method comprises a step of recovering the polyester at the end of the polymerization step. The semi-crystalline thermoplastic polyester thus recovered can then be shaped as described above.

According to a variant of the synthesis process, a step of increasing molar mass is carried out after the step of recovering the semi-crystalline thermoplastic polyester.

The step of increasing the molar mass is carried out by post-polymerization and can consist of a step of polycondensation in the solid state (PCS) of the semi-crystalline thermoplastic polyester or in a step of reactive extrusion of the semi-thermoplastic polyester crystalline in the presence of at least one chain extender.

Thus, according to a first variant of the manufacturing process, the post-polymerization step is carried out by PCS.

The PCS is generally carried out at a temperature between the glass transition temperature and the polymer melting temperature. Thus, to carry out the PCS, it is necessary that the polymer is semi-crystalline. Preferably, the latter has a heat of fusion greater than 10 J / g, preferably greater than 20 J / g, the measurement of this heat of fusion consisting in subjecting a sample of this polymer of reduced viscosity in lower solution a heat treatment at 170 ° C. for 16 hours then evaluating the heat of fusion by DSC by heating the sample to 10 K / min.

Advantageously, the PCS stage is carried out at a temperature ranging from 190 to 280 ° C., preferably ranging from 200 to 250 ° C., this stage must imperatively be carried out at a temperature below the melting temperature of the semi-thermoplastic polyester. crystalline.

The PCS stage can be carried out in an inert atmosphere, for example under nitrogen or under argon or under vacuum.

According to a second variant of the manufacturing process, the post-polymerization step is carried out by reactive extrusion of the semi-crystalline thermoplastic polyester in the presence of at least one chain extender.

The chain extender is a compound comprising two functions capable of reacting, in reactive extrusion, with functions, alcohol, carboxylic acid and / or carboxylic acid ester of the semi-crystalline thermoplastic polyester. The chain extender can for example be chosen from the compounds comprising two isocyanate, isocyanurate, lactam, lactone, carbonate, epoxy, oxazoline and imide functions, said functions being able to be identical or different. The chain extension of the thermoplastic polyester can be carried out in all reactors capable of mixing a very viscous medium with sufficiently dispersive stirring to ensure a good interface between the molten material and the gas overhead of the reactor. A reactor particularly suitable for this treatment stage is extrusion.

Reactive extrusion can be carried out in an extruder of any type, in particular a single-screw extruder, a co-rotating twin-screw extruder or a contra-rotating twin-screw extruder. However, it is preferred to carry out this reactive extrusion using a co-rotary extruder.

• introduisant le polymère dans l'extrudeuse de manière à faire fondre ledit polymère ;
• puis introduisant dans le polymère fondu l'allongeur de chaîne ;
• puis faisant réagir dans l'extrudeuse le polymère avec l'allongeur de chaîne ;
• puis récupérant le polyester thermoplastique semi-cristallin obtenu à l'étape d'extrusion.

The reactive extrusion step can be done by:

• introducing the polymer into the extruder so as to melt said polymer;
• then introducing into the molten polymer the chain extender;
• then reacting the polymer in the extruder with the chain extender;
• then recovering the semi-crystalline thermoplastic polyester obtained in the extrusion step.

During extrusion, the temperature inside the extruder is adjusted to be higher than the melting temperature of the polymer. The temperature inside the extruder can range from 150 ° C to 320 ° C.

The semi-crystalline thermoplastic polyester obtained after the step of increasing the molar mass is recovered and then shaped as described above.

The invention will be better understood with the aid of the examples and figures below which are intended to be purely illustrative and in no way limit the scope of the protection.

Examples

The properties of polymers have been studied with the following techniques:

Reduced viscosity in solution

The reduced viscosity in solution is evaluated using an Ubbelohde capillary viscometer at 25 ° C in an equimassic mixture of phenol and ortho-dichlorobenzene after dissolution of the polymer at 130 ° C with stirring, the concentration of polymer introduced being 5g / L.

DSC

The thermal properties of the polyesters were measured by differential scanning calorimetry (DSC): The sample is firstly heated under nitrogen in an open crucible from 10 to 320 ° C (10 ° C.min-1) , cooled to 10 ° C (10 ° C.min-1) then reheated to 320 ° C under the same conditions as the first step. The glass transition temperatures were taken at the mid-point of the second heating. The possible melting temperatures are determined on the endothermic peak (start of the peak (onset)) at the first heating.

Similarly, the determination of the enthalpy of fusion (area under the curve) is carried out on the first heating.

For the illustrative examples presented below, the following reagents were used: 1,4-Cyclohexane dimethanol (purity 99%, mixture of cis and trans isomers)
Isosorbide (purity> 99.5%) Polysorb® P from Roquette Frères
Terephthalic acid (purity 99 +%) from Acros
Irganox® 1010 from BASF AG
Dibutyltin oxide (purity 98%) from Sigma Aldrich

Example 1: Preparation of a semi-crystalline thermoplastic polyester and use for the manufacture of bi-oriented film. A: Polymerization

Two thermoplastic polyesters P1 and P2 were prepared.

The first semi-crystalline thermoplastic polyester P1 was prepared according to the procedure below, for use according to the invention with in particular a molar ratio of 1,4: 3,6-dianhydrohexitol units (A) / sum of units 1, 4: 3,6-dianhydrohexitol (A) and alicyclic diol units (B) other than 1,4: 3,6-dianhydrohexitol units (A) of at least 0.05 and at most 0.30.

Thus, in a 7.5L reactor are added 1432 g (9.9 mol) of 1,4-cyclohexanedimethanol, 484 g (3.3 mol) of isosorbide, 2000 g (12.0 mol) of terephthalic acid , 1.65 g of Irganox 1010 (antioxidant) and 1.39 g of dibutyltinoxide (catalyst). To extract residual oxygen isosorbide crystals, 4 vacuum-nitrogen cycles are carried out once the temperature of the reaction medium is between 60 and 80 ° C.

The reaction mixture is then heated to 275 ° C (4 ° C / min) under 6.6 bar of pressure and with constant stirring (150 rpm) until an esterification rate of 87% is obtained (estimated from of the mass of distillate collected). Then, the pressure is reduced to 0.7 mbar in 90 minutes according to a logarithmic ramp and the temperature brought to 285 ° C.

These vacuum and temperature conditions were maintained until an increase in torque of 12.1 Nm was obtained compared to the initial torque.

Finally, a rod of polymer is poured through the bottom valve of the reactor, cooled in a tank of thermo-regulated water at 15 ° C and cut into the form of granules of approximately 15 mg.

The resin thus obtained has a reduced viscosity in solution of 80.1 ml / g.

Analysis by ¹ H NMR of the polyester shows that the final polyester contains 17.0 mol% of isosorbide relative to the diols. With regard to the thermal properties, the polymer has a glass transition temperature of 96 ° C, a melting temperature of 253 ° C with an enthalpy of fusion of 23.2 J / g.

The second thermoplastic polyester P2 was prepared according to the same procedure as the semi-crystalline thermoplastic polyester P1.

This second polyester P2 is a polyester used for comparison and thus has a molar ratio [A] / ([A] + [B]) of 0.44. The amounts used in compounds are detailed in Table 1 below:

The resin thus obtained with polyester P2 has a reduced viscosity in solution of 54.9 ml / g.

With regard to thermal properties, polyester P2 has a glass transition temperature of 125 ° C., and does not exhibit an endothermic melting peak in analysis differential scanning calorimetry even after a heat treatment of 16h at 170 ° C which indicates its amorphous nature.

B: Formatting

The polyester granules P1 and P2 obtained in step A of polymerization are dried under vacuum at 140 ° C for P1 and 110 ° C for P2 in order to reach residual moisture levels of less than 300 ppm, in this example, the water content of the granules is 180 ppm.

The granules maintained in a dry atmosphere are then introduced into the hopper of the extruder.

The extruder used is a Collin extruder equipped with a flat die, the assembly is completed by a calendering machine. The extrusion parameters are grouped in Table 2 below: <b> Table 2 </b> Settings Units Values Temperature (feed -> sector) ° C 250/265/275/275/280 (P1) 220/235/245/245/250 (P2) Screw rotation speed rpm 80 Roller temperature ° C 40

The sheets thus extruded from polyester P1 and P2 have a thickness of 4 mm.

The sheets are then cut into squares of size 11.2x11.2 cm and then, using a Karo IV stretching machine of the Brückner brand, the cutouts of the sheets are stretched in two directions at a temperature of 130 ° C to 140 ° C with a stretch ratio of 2.8x2.8 and in 2 seconds in both directions. One thus obtains a bi-oriented film obtained having a thickness of 14 μm.

The bi-oriented films thus obtained from polyesters P1 and P2 have very different properties.

Indeed, the polyester P1 makes it possible to obtain a bi-oriented film whose crystal structure has been verified by diffraction / scattering of X-rays characteristic of crystallization under stress during a bi-stretching phase. The bi-oriented film obtained has good mechanical properties.

On the contrary, when the polyester P2 is extruded it does not have the possibility of being structured so as to reveal a crystalline structure. This absence of crystal structure makes it brittle and requires a greater thickness to be able to be used, thus leading to a more restricted range of applications. Indeed, this film cannot undergo bi-orientation treatment on the Karo IV machine without being destroyed.

Example 2: Preparation of bi-oriented films A: Preparation

Two other semi-crystalline polyesters P3 and P4 according to the invention were prepared according to the same procedure as in Example 1. The amounts of the various compounds were adapted so as to obtain the polyesters P3 and P4 having respectively 15% by moles and 25% by moles of isosorbide.

The amounts were determined by ¹ H RMM and the amounts are expressed as a percentage relative to the total amount of diols in the polyester.

The reduced viscosity in solution The polyesters P3 and P4 are respectively 75 mUg and 63 mL / g.

B: Leaf shaping

The polyester granules P3 and P4 obtained in step A are then dried for 5 hours at 150 ° C. and have a water content of 0.074% by weight and 0.085% by weight respectively.

The granules maintained in a dry atmosphere are then introduced into the hopper of the extruder. The extruder used is a Collin extruder equipped with a flat die, the assembly is completed by a calendering machine. The extrusion parameters are grouped in Table 3 below: <b> Table 3 </b> Settings Units Values Temperature (feed -> sector) ° C 210/260/275/295/275 (P3) 210/240/255/275/255 (P4) 210/255/270/290/260 (P4) 210/265/280/300/270 (P4) Screw rotation speed rpm 50 Roller temperature ° C 55

The sheets thus extruded from polyester P3 and P4 have a thickness of 350 μm.

C: Biaxial stretching

The sheets obtained above are cut into squares of dimension 12x12 cm and then stretched using a Karo IV stretching machine from Brückner brand. The stretching parameters for each polyester are given below: <b> Table 4 </b> Settings P3 sheets P4 sheets Preheating 2 min 2 min Setpoint temperature of the machine 125 ° C (measured 134 ° C) 135 ° C (measured 138 ° C) Draw rate λ = 2 ^∗ 2 λ = 3 ^∗ 3 λ = 3 ^∗ 3 λ = 3.5 ^∗ 3.5 λ = 3.2 ^∗ 3.2

The drawing speeds were adapted so as to obtain 100% drawing for the sheets obtained with polyester P3 and 50% drawing for the sheets obtained with polyester P4. The stretching time is 2 seconds.

Several bi-oriented films have thus been manufactured and have thicknesses varying from 20 μm to 110 μm depending on the stretching rates. All of the bi-oriented films are transparent, of shiny appearance and the stretching is homogeneous.

As the examples show, the semi-crystalline thermoplastic polyester according to the invention is an excellent alternative for the production of bi-oriented films having good mechanical properties.

Claims (25)

1. The use of a semicrystalline thermoplastic polyester for producing biaxially oriented films, said polyester comprising:

   • at least one 1,4:3,6-dianhydrohexitol unit (A);

   • at least one alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A);

   • at least one terephthalic acid unit (C);

   wherein the (A)/[(A)+(B)] molar ratio is at least 0.05 and at most 0.30;
   said polyester not containing any aliphatic non-cyclic diol units or comprising a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 5%, and the reduced viscosity in solution (25°C; phenol (50%m): ortho-dichlorobenzene (50%m); 5 g/l of polyester) of said polyester being greater than 50 ml/g.
2. The use as claimed in claim 1, characterized in that the alicyclic diol (B) is a diol chosen from 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol or a mixture of these diols, very preferentially 1,4-cyclohexanedimethanol.
3. The use as claimed in either one of claims 1 and 2, characterized in that the 1,4:3,6-dianhydrohexitol (A) is isosorbide.
4. The use as claimed in any one of claims 1 to 3, characterized in that the polyester does not contain any aliphatic non-cyclic diol units, or comprises a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 1%, preferably the polyester does not contain any aliphatic non-cyclic diol units.
5. The use as claimed in any one of claims 1 to 4, characterized in that the (3,6-dianhydrohexitol unit (A) + alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A))/(terephthalic acid unit (C)) molar ratio is from 1.05 to 1.5.
6. The use as claimed in any one of claims 1 to 5, characterized in that the biaxially oriented film has a thickness of from 10 µm to 250 µm.
7. The use as claimed in any one of claims 1 to 6, characterized in that the biaxially oriented film comprises one or more additional polymers and/or one or more additives.
8. The use as claimed in any one of claims 1 to 7, characterized in that the biaxially oriented film is treated by a corona treatment, a metallization treatment or a plasma treatment.
9. A biaxially oriented film comprising a semicrystalline thermoplastic polyester comprising:

   • at least one 1,4:3,6-dianhydrohexitol unit (A);

   • at least one alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A);

   • at least one terephthalic acid unit (C);

   wherein the (A)/[(A)+(B)] molar ratio is at least 0.05 and at most 0.30;
   said polyester not containing any aliphatic non-cyclic diol units or comprising a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 5%, and the reduced viscosity in solution (25°C; phenol (50%m): ortho-dichlorobenzene (50%m); 5 g/l of polyester) of said polyester being greater than 50 ml/g.
10. The biaxially oriented film as claimed in claim 9, characterized in that the alicyclic diol (B) is a diol chosen from 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol or a mixture of these diols, very preferentially 1,4-cyclohexanedimethanol.
11. The biaxially oriented film as claimed in either of claims 9 and 10, characterized in that the 1,4:3,6-dianhydrohexitol (A) is isosorbide.
12. The biaxially oriented film as claimed in one of claims 9 to 11, characterized in that the polyester does not contain any aliphatic non-cyclic diol units, or comprises a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 1%, preferably the polyester does not contain any aliphatic non-cyclic diol units.
13. The biaxially oriented film as claimed in one of claims 9 to 12, characterized in that the (3,6-dianhydrohexitol unit (A) + alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A))/(terephthalic acid unit (C)) molar ratio is from 1.05 to 1.5.
14. The biaxially oriented film as claimed in one of claims 9 to 13, characterized in that the biaxially oriented film has a thickness of from 10 µm to 250 µm.
15. The biaxially oriented film as claimed in one of claims 9 to 14, characterized in that the biaxially oriented film comprises one or more additional polymers and/or one or more additives.
16. The biaxially oriented film as claimed in one of claims 9 to 15, characterized in that the biaxially oriented film is treated by a corona treatment, a metallization treatment or a plasma treatment.
17. A process for producing a biaxially oriented film, comprising the following steps of:

    • provision of a semicrystalline thermoplastic polyester comprising at least one 1,4:3,6-dianhydrohexitol unit (A), at least one alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A), at least one terephthalic acid unit (C), wherein the (A)/[(A)+(B)] molar ratio is at least 0.05 and at most 0.30, said polyester not containing any aliphatic non-cyclic diol units or comprising a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 5%, and the reduced viscosity in solution (25°C; phenol (50%m): ortho-dichlorobenzene (50%m); 5 g/l of polyester) of said polyester being greater than 50 ml/g;

    • preparation of said biaxially oriented film from the semicrystalline thermoplastic polyester obtained in the preceding step.
18. The production process as claimed in claim 17, characterized in that the preparation step is carried out by the cast extrusion method, and in particular by the Stenter process.
19. The production process as claimed in claim 17 or 18, characterized in that the alicyclic diol (B) is a diol chosen from 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol or a mixture of these diols, very preferentially 1,4-cyclohexanedimethanol.
20. The production process as claimed in any one of claims 17 to 19, characterized in that the 1,4:3,6-dianhydrohexitol (A) is isosorbide.
21. The production process as claimed in any one of claims 17 to 20, characterized in that the polyester does not contain any aliphatic non-cyclic diol units, or comprises a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 1%, preferably the polyester does not contain any aliphatic non-cyclic diol units.
22. The production process as claimed in any one of claims 17 to 21, characterized in that the (3,6-dianhydrohexitol unit (A) + alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A))/(terephthalic acid unit (C)) molar ratio is from 1.05 to 1.5.
23. The production process as claimed in any one of claims 17 to 22, characterized in that the biaxially oriented film has a thickness of from 10 µm to 250 µm.
24. The production process as claimed in any one of claims 17 to 23, characterized in that the biaxially oriented film comprises one or more additional polymers and/or one or more additives.
25. The production process as claimed in any one of claims 17 to 24, characterized in that the biaxially oriented film is treated by a corona treatment, a metallization treatment or a plasma treatment.